Mackie CR4 amplifier no sound

[UserXP]

Re: Mackie CR4 amplifier no sound

Sorry for the long delay, I was unable to find some spare time to do this.

I managed to reproduce the state like when the amplifier was connected for the first time and when the sound died after a couple of seconds! But only once. Here's what I've done:

First, I desoldered the TDA's Pin 5.
I connected the amplifier's PCB to the speaker housing peripherals fully.

I turned on the speakers and, normally, there was a loud pop sound because Pin 5 was disconnected, but the speakers did produce sound (so the amplifier chip seems to be OK). The mute function was obviously not engaged because of the disconnected Pin 5, so the pop sounds were there. However, something interesting happened; I left Pin 5 unsoldered, so I would be able to make contact with its solder joint with a small isolated screwdriver. To my surprise, while making the contact with a screwdriver, the speaker continued to play sound and the Mute circuit did not interfere. To test this, since it was working, upon switching the speakers on, there was no loud pop sound and after a second or two the amplifier kicked in and started to play the sound. Upon inserting the phones, the sound cut off - all this verifies that the mute circuit was sending the correct voltage to TDA's Pin 5.

However, after a while, the sound started to fade again until it was all gone again. Only this time, fiddling with Pin 5 did not make a difference: When Pin 5 is disconnected, there is sound, there is also that loud pop sound, and no mute function: if Pin 5 is reconnected, there is no sound coming from the speakers.
So I heard the amplifier working again the way it is supposed to for only that amount of time, until it "died" again.
If I leave the speakers completely turned off for a while and try again, there is a very short interval when the sound appears and then cuts off completely (all this while TDA's Pin5 is in contact).

The measurements below are at the point when the speaker were operational:

LINE A (the signal coming from the phonejack Pin 5 on CN3B):

When TDA PIN5 is RESET:

For about 10 seconds, measurements are:
When Phonejack is disconnected: 12.01V
When Phone Jack is connected: 000.2mV
The Mackie guy said that this is a normal operation.
After 10 seconds, the Speaker volume reduced, but measurements remained the same!
If the phone jack is connected, the volume on the headphones remains but when disconnected, the sound from the speakers is not restored.

LINE B (Mute circuit going to TDA's Pin5)
When TDA PIN5 is disconnected
Measurements are 000.5mV on PIN5 and the speaker plays sound, irrespective of the phone jack presence!

LINE C
I was unable to locate R87! I can see R86 on the leads side and R88 on the other side of the PCB.

Does this shed any light on the source of the problem? It worked again and then as if something got depleted and the speakers went mute again. Is there an electrolytic capacitor that might be a possible issue?

I'd really like to repair this amplifier. While it was working for that short period of time, I was able to test the L/R switch and it worked perfectly, no cracklings or one of the speakers losing sound - it works great. Also the PCB is not burnt in the problematic area. Cosmetically, it is in a much better condition than my original PCB - only, it doesn't work well.

All this looks like there is one tiny component at fault, making this work-not work annoying issue. Please, let's try to identfy it together.

[petehall347]

Re: Mackie CR4 amplifier no sound

where does that line go thats marked A ?

[petehall347]

Re: Mackie CR4 amplifier no sound

what voltages are at the +-12v points ?

[budm]

Re: Mackie CR4 amplifier no sound

What are the Blue and Red readings?
Are they your readings or what Mackie tells you what they should be?
The Voltage readings in Blue are what you should have after the unit is turned on.
Q1 abd Q2 are part of the soft-start that keeps the IC in Mute mode when the unit is first turned on so it will not produce pop to the speaker.
BTW, I also do not see your reply about the Voltage on the pin 5 of the IC with and without phone plug.

[UserXP]

Re: Mackie CR4 amplifier no sound

Hi, all.
I actually got a portion of the CR schematics from Mackie's authorized service. They sent this portion and suspect that either TDA's Pin5 is constatntly fed full voltage, whereas it should be at around 12V in order for the sound to work.
He also suggested disconnecting it, but I would like to fully repair this.
The image suggests that I should check a resistor in this area and if it reads a faulty negative voltage, then to cut it and it will eliminate the soft start (what ever that means).

[budm]

Re: Mackie CR4 amplifier no sound

Yes, I shorted pins 4 and 5 for the phonejack plug.
Of course I didn't short the TDA7265 chip. But, I did some more measurements of its pins, here are the voltages:

Pin1 = -21.43V
Pin2 = -040.6 mV
Pin3 = +21.43V
Pin4 = -018.0mV
Pin5 = +20.70V
Pin6 = -21.43V
Pin7 = +000.0mV
Pin8 = -000.0mV
Pin9 = +000.0mV
Pin10 = -001.7mV
Pin11 = +0.000mV

So pin 5 stays at 20.70V with or without phone connected, correct?
For the AMP to be in play mode pin 5 has to be < +Vs - 6V (per IC spec sheet) = +21.43V - 6V = +15.43V or less.
How about the Voltages of the working amplifier?

Does your board have Q1 and Q2 as shown in the schematic?
https://www.badcaps.net/forum/attach...7&d=1603093112

[petehall347]

Re: Mackie CR4 amplifier no sound

ok you posted it .. its quite simple really .... i might start with seeing if z1 was shorted .
https://www.badcaps.net/forum/attach...1&d=1603093112

[petehall347]

Re: Mackie CR4 amplifier no sound

could desolder it for testing purposes .
could do with the circuit diagram for whatever controls pin 5 voltages .

[UserXP]

Re: Mackie CR4 amplifier no sound

it is muted ... Pin5 = +20.70V
you could try the disconnecting pin 5 trick or search for why its being sent 20.7v .

I would definitively like to find the cause of it and fix it, so the mute function is operational as intended.
Cutting / desoldering Pin 5 wouldn't be a fix, but rather a workaround, with a broken mute function (if successful).

[petehall347]

Re: Mackie CR4 amplifier no sound

it is muted ... Pin5 = +20.70V
you could try the disconnecting pin 5 trick or search for why its being sent 20.7v .

[UserXP]

Re: Mackie CR4 amplifier no sound

Yes, I shorted pins 4 and 5 for the phonejack plug.
Of course I didn't short the TDA7265 chip. But, I did some more measurements of its pins, here are the voltages:

Pin1 = -21.43V
Pin2 = -040.6 mV
Pin3 = +21.43V
Pin4 = -018.0mV
Pin5 = +20.70V
Pin6 = -21.43V
Pin7 = +000.0mV
Pin8 = -000.0mV
Pin9 = +000.0mV
Pin10 = -001.7mV
Pin11 = +0.000mV

[petehall347]

Re: Mackie CR4 amplifier no sound

Why did you short pin 4 to pin 5? You do know what the circuit ground is, correct?
Pin 4 is the AMPLIFIER OUTPUT PIN! Look at the IC spec sheet.
I hope you did not damage the IC.

Since you have working amplifier so why don't you check the Voltage at pin 5?

think he means pin 4 and 5 at socket switch .

[budm]

Re: Mackie CR4 amplifier no sound

Hmmm... I shorted pins 4 and 5, measured the voltage on TDA's pin 5 at 20.9V.
With pins 4 and 5 open the voltage is the same.

I did this on the PCB alone, with internal speakers and front connectors cables disconnected. Can that influence the measurements?

Why did you short pin 4 to pin 5? You do know what the circuit ground is, correct?
Pin 4 is the AMPLIFIER OUTPUT PIN! Look at the IC spec sheet.
I hope you did not damage the IC.

Since you have working amplifier so why don't you check the Voltage at pin 5?

[UserXP]

Re: Mackie CR4 amplifier no sound

Hmmm... I shorted pins 4 and 5, measured the voltage on TDA's pin 5 at 20.9V.
With pins 4 and 5 open the voltage is the same.

I did this on the PCB alone, with internal speakers and front connectors cables disconnected. Can that influence the measurements?

[momaka]

Re: Mackie CR4 amplifier no sound

OK, please explain. I am to put the multimeter to DC voltage check and touch pin 5 and GND with the probes?

Yup, do that to verify if the chip is going into mute state or not. Report what voltage you see and whether that's with the amp working or not.

[budm]

Re: Mackie CR4 amplifier no sound

Mute pin function, see PDF. It is not just LO or HI, it has Standby mode, Mute mode, and Play mode.

MUTE STAND-BY FUNCTION
The pin 5 (MUTE/STAND-BY) controls the amplifier
status by two different thresholds, referred to
+VS.
- When Vpin5 higher than = +VS - 2.5V the
amplifier is in Stand-by mode and the final
stage generators are off.

- when Vpin5 is between +VS - 2.5V and +VS
- 6V the final stage current generators are
switched on and the amplifier is in mute
mode
- when Vpin5 is lower than +VS - 6V the amplifier
is play mode.

[budm]

Re: Mackie CR4 amplifier no sound

The voltage on pin 5 of the TDA7265 is around 21V when 4 and 5 pins if the phonejack make contact.

It should change state when headphone is plugged in and out.

[UserXP]

Re: Mackie CR4 amplifier no sound

The voltage on pin 5 of the TDA7265 is around 21V when 4 and 5 pins if the phonejack make contact.

[budm]

Re: Mackie CR4 amplifier no sound

Then you have to verify that pin 4 and 5 are making contact all the way to the amplifier mute pin by checking Voltage (Black probe on circuit ground, red probe on pin 5) on mute pin of the IC when phone jack is in and when removed, it should change state.
Having full schematic will also help.

[UserXP]

Re: Mackie CR4 amplifier no sound

Yes, it does make contact because the original amplifier PCB has no problems with the phonejack. It enters the mute mode when headphones are plugged in, and plays the sound again immidiately after the headphones are removed from the jack - just the way it is supposed to. So pins 4 and 5 obviously make contact on headphones plug removal.

Everything mounted on the front panel of the powered speaker works perfectly with the original amplifier.
When the same front panel is connected to the "new" amplifier, there is no sound. Therefore, it must be something on this new amplifier's PCB that's bad. The phonejacks are fine.